1. Field of the Invention
The present invention generally relates to systems for testing contact holes in integrated circuit devices and more particularly to a system using a scanning electron microscope to test contact holes.
2. Description of the Related Art
Contact holes in integrated circuit devices (e.g., semiconductor devices) allow vertical interconnections between various layers. Inspection of the bottom of contact holes is difficult due to the high aspect ratios of such holes. Holes with high aspect ratios are generally very deep relative to their width. Thus, the aspect ratio generally increases as devices are continually made smaller and contact hole diameters shrink.
Conventional systems that determine whether contacts holes are open at the bottom involve a destructive cross-sectional inspection using a high voltage scanning electron microscope (SEM), where the contacts are cleaved in half and imaged perpendicular to the contact axis. This method is expensive, time-consuming, and unable to provide timely feedback to the contact processes. The invention overcomes these problems, as discussed below.
It is, therefore, an object of the present invention to provide a structure and method for inspecting a plurality of similar structures in the surface of a workpiece, wherein the method includes providing a workpiece having a plurality of regions, each of the regions including at least two different materials, generating an image from each of the regions such that an image contrast between the two materials is enhanced and classifying the images into at least two classes including an acceptable class of images and unacceptable class of images.
The generating process is performed by applying a scanning electron microscope to the regions. The classifying includes determining, on a graduated scale, an amount of acceptability of the images.
The regions are contact openings and the acceptable class of images includes opened contact openings and the unacceptable class of images includes closed contact openings. The classifying includes determining, on a graduated scale, an amount the contact openings are opened.
Another embodiment of the invention is a method of inspecting openings extending through a first layer of a structure to a second layer of the structure, where the method includes positioning an electron microscope above the structure, generating an electric field between the structure and the electron microscope, and scanning the structure with the electron microscope to generate an image of the structure, wherein the first layer appears differently than the second layer, such that openings extending through the first layer to the second layer appear as contrasting features in the image.
The openings have a pattern and the method further comprises identifying ones of the openings that do not extend fully through the first layer, based on the pattern. Also, the invention determines, on a graduated scale, an amount that the openings extend through the first layer. The process of identifying ones of the openings that do not extend fully through the first layer comprises automatically evaluating the images using a computer system.
In one example, the structure comprises a semiconductor device and the openings comprise contact openings. The invention also includes selecting the first layer and the second layer to contrast each other on the image. The scanning process includes scanning a portion of the image in one of an xe2x80x9cXxe2x80x9d pattern and a xe2x80x9cYxe2x80x9d pattern.
Another embodiment of the invention is a computer system, tangibly embodying a program of instructions executable by the machine to perform a method of inspecting openings extending through a first layer of a structure to a second layer of the structure, where the method comprises positioning an electron microscope above the structure, generating an electric field between the structure and the electron microscope and scanning the structure with the electron microscope to generate an image of the structure, wherein the first layer appears differently than the second layer, such that openings extending through the first layer to the second layer appear as contrasting features in the image.
Benefits of the invention include substantially improved feedback time to the etch processes to improve etch quality. Also, the invention is able to inspect a much larger sample of chips/wafers than destructive cross-sectioning can, to enable a more complete picture of etch quality.